1. Field of the Invention
The present invention relates generally to power supplies that include voltage-regulated direct current-to-direct current (xe2x80x9cDC/DCxe2x80x9d) converters, and more particularly to reducing transient voltage excursions in output power delivered by such power supplies.
2. Description of the Prior Art
In numerous different applications, electrical power supplies, that include a voltage-regulated DC/DC converter, must accommodate substantial changes in electrical current drawn by a load coupled thereto that occur during a short interval of time. Because the voltage regulated DC/DC converter cannot instantaneously adjust its operation to compensate for a sudden, substantial change in the electrical current drawn by a load, for a short interval of time following such a load change the voltage of electrical power produced by the DC/DC converter may increase or decrease depending upon whether the load decreased or increased.
FIG. 1 depicts a power supply, referred to by the general reference character 20, that implements a conventional approach for reducing transient voltage excursions in output power produced by a voltage-regulated DC/DC power converter 22 when electrical current drawn by a load changes. As depicted in FIG. 1, the DC/DC power converter 22 of the conventional power supply 20 receives input power at an input voltage Vin via an input-power line 24. Energized by electrical power received via the input-power line 24, the voltage-regulated DC/DC power converter 22 of the power supply 20 supplies an electrical current iout from an output 25 to a load 26 via an output-power line 28. Moreover, the DC/DC power converter 22 includes circuits for regulating output-power voltage vout present on the output-power line 28 so that, for a specific configuration of the power supply 20, the output-power voltage vout may be equal to a reference voltage vref that the DC/DC power converter 22 receives via a reference-voltage line 32. For other possible configurations of the power supply 20, the output-power voltage vout may be greater than or less than the reference voltage vref.
To reduce transient changes in the output-power voltage vout (e.g. xc2x150 millivolts in an interval of 50 to 100 nanoseconds) caused by sudden, substantial changes in the electrical current iout drawn by the load 26, the conventional power supply 20 also includes a filter capacitor 34. The filter capacitor 34 connects in parallel with the load 26 between the output-power line 28 and circuit ground 36. To effectively reduce such transient changes in the output-power voltage vout, the filter capacitor 34 must possess a large capacitance, and exhibit a low equivalent series resistance (xe2x80x9cESRxe2x80x9d). Because the filter capacitor 34 in a conventional power supply 20 must possess these electrical characteristics, such capacitors are, in general, physically large and comparatively expensive.
Accordingly, it would be advantageous to find a physically smaller and cheaper way to reduce transient changes in the output-power voltage vout caused by sudden, substantial changes in the electrical current iout drawn by the load 26 than the conventional filter capacitor 34. While an ability to achieve an equivalent reduction in transient changes in the output-power voltage vout from the power supply 20 that is smaller and less expensive is generally advantageous, such a capability is particularly advantageous for compact systems that occupy a limited amount of space such as laptop and notebook portable computers.
An object of the present invention is to provide a smaller power supply that includes a DC/DC converter.
Another object of the present invention is to provide a more economical power supply that includes a DC/DC converter.
Another object of the present invention is to provide a smaller power supply that is capable of reducing transient changes in output-power voltage vout caused by sudden, substantial changes in the electrical current iout drawn by a load.
Briefly, the present invention in one embodiment is a power supply that includes both a voltage-regulated power converter and an active transient-control circuit. The voltage-regulated power converter:
1. receives input electrical power having an input-power voltage which possesses both a polarity and magnitude; and
2. produces output electrical power at an output of the power converter having output-power voltage vout which possesses both a pre-established polarity and magnitude.
The output electrical power thus produced is adapted to be supplied to a load coupled to the power supply. In a preferred embodiment of the present invention, the voltage-regulated power converter provides output electrical power having a voltage which possesses:
1. a polarity identical to that of the input electrical power; and
2. a magnitude that is less than the input-power voltage of the input electrical power present in the power supply.
The active transient-control circuit included in the power supply responds swiftly to changes occurring in the output-power voltage produced by the power converter to reduce transient changes in the output-power voltage vout caused by sudden, substantial changes in the electrical current iout drawn by the load. To respond in this way, when the output-power voltage has a magnitude less than a lower pre-established-voltage threshold, the active transient-control circuit supplies electrical energy directly to the load from the input electrical power thereby augmenting output electrical power supplied to the load by the power converter. Correspondingly, when the output-power voltage has a magnitude that exceeds an upper pre-established-voltage threshold, the active transient-control circuit draws electrical energy directly from the output of the power converter.
In a particularly preferred embodiment of the present invention, the active transient-control circuit augments output electrical power supplied to the load by the power converter only while such electrical current does not exceed a pre-established threshold for augmenting electrical current suppliable to the load. Correspondingly, in this particularly preferred embodiment the active transient-control circuit draws electrical energy directly from the output of the power converter only while electrical current drawn therefrom does not exceed a pre-established threshold or electrical current drawable from the output of said power converter.
An advantage of the present invention is that it permits using a substantially smaller filter capacitor.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.